Playing with Functional Attributes
Posted by jeffhobbs on October 4, 2007
I was playing with the DOTDENSITY functional attribute today. Although it’s quite easy to use, I’m not sure how many people have ever actually used it.
It’s defined as "Returns a collection of points that are placed on that area". Basically, you can tell GeoMedia to place a number of dots on a polygon and these number of dots are designed to show density. The more dots, the greater the density. I’ve typically seen this done with populations. So, to make life simple and easy to share with my readers, I did a little playing with the US Sample data set. You can download my geoworkspace from here. The geoworkspace should work fine if you have the US Sample data set in c:\warehouses. If you’ve moved it, just be sure to change the location of the warehouse under Warehouse > Connections.
In short, I normalized the population by dividing the populations for Asians, Blacks, and Whites. I did this by dividing each population by 10,000. This functional attribute looked like ROUND(Input.WHPOP/10000, 0). This was done just to simply reduce the number of dots. After that, I created the functional attribute: DOTDENSITY(Input.Geometry, INT(Output.WHITE)). This simply takes the output from my previous functional attribute that divided the white population by 10,000 (Output.WHITE) and rounded it to the nearest whole number (INT function). After that I feed in the input geometry and the rounded Output.WHITE population into the DOTDENSITY function. The result is a point collection for each of the black, white, and asian populations.
You can take a look at my screenshots of California to see the results:
All of the dots:
White dot = White Population
Black dot = Black Population
Blue dot = Asian Population
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